In hard disk drives, data is written to and read from magnetic recording media, herein called disks. Typically, one or more disks having a thin film of magnetic material coated thereon are rotatably mounted on a spindle. A read/write head mounted on an actuator arm is positioned in close proximity to the disk surface to write data to and read data from the disk surface.
During operation of the disk drive, the actuator arm moves the read/write head to the desired radial position on the surface of the rotating disk where the read/write head electromagnetically writes data to the disk and senses magnetic field signal changes to read data from the disk. Usually, the read/write head is integrally mounted in a carrier or support referred to as a slider. The slider generally serves to mechanically support the read/write head and any electrical connections between the read/write head and the disk drive. The slider is aerodynamically shaped, which allows it to fly over and maintain a uniform distance from the surface of the rotating disk.
Typically, the read/write head includes a magnetoresistive read element to read recorded data from the disk and an inductive write element to write the data to the disk. The read element includes a thin layer of a magnetoresistive sensor stripe sandwiched between two magnetic shields that may be electrically connected together but are otherwise isolated. A current is passed through the sensor stripe, and the resistance of the magnetoresistive stripe varies in response to a previously recorded magnetic pattern on the disk. In this way, a corresponding varying voltage is detected across the sensor stripe. The magnetic shields help the sensor stripe to focus on a narrow region of the magnetic medium, hence improving the spatial resolution of the read head.
The write element typically includes a coil of wire through which current is passed to create a magnetic field that can be directed toward an adjacent portion of the disk by a ferromagnetic member known as a write pole. While it is known that the write element can be arranged to either store data longitudinally or perpendicularly on the disk, most, if not all, commercial disk drives to date have utilized longitudinal recording arrangements. Although perpendicular recording techniques have the potential to allow for higher densities of recorded information, longitudinal recording is used in all current products for historical reasons. An early perpendicular recording technique is disclosed in U.S. Pat. No. RE 33,949, the contents of which are incorporated herein by reference.
The '949 patent discloses a perpendicular or vertical write head with a write pole section, a downstream shield section, and a pancake coil surrounding the write pole section to generate magnetic flux therein. The shield section is disclosed to have a surface facing toward the media that is many times larger than a similarly-oriented face of the write pole. The media is disclosed to include two layers, an upper layer closer to the head having perpendicular uniaxial anisotropy and a lower layer having low magnetic reluctance (now known as the Soft Under Layer (SUL)). A high write field can then be produced between the write pole and the SUL to record information in the upper layer of the media. The write flux returns through the SUL to the downstream write shield. The return field for this design was predicted to be much lower than the write field because of the larger area of the face of the write shield as compared to the face of the write pole. It was recognized that the return field needed to be sufficiently low so as not to erase the downstream information/data under the write shield.
It is believed that to date all read/write heads in disk drives have featured sliders with a substrate with the read element built on top thereof, and then a write element produced on top of the read element. While this geometric arrangement is completely standard in the industry, it does have certain disadvantages. One class of disadvantages relates to manufacturing processes. It turns out that the read element has the potential to be more adversely affected by subsequent manufacturing processes than does the write element. For example, in producing the read and write elements it is commonly necessary to anneal magnetic materials therein by subjecting them to high temperatures and high magnetic fields for an extended period of time. Modern read elements are limited in the extent to which they can withstand typical annealing temperatures and magnetic fields. Because of this, there are significant constraints that are placed on the manufacturing processes that are subsequent to the read element being deposited onto the substrate. These significant constraints can impact the ability to manufacture the write element in the desired manner.
Another class of disadvantages of placing the read element under the write element relates to heat distribution. It turns out that the write element is the greatest source of heat in the read/write head. The two routes most commonly used for dissipating heat from the head are either through the slider or through the media (the disk surface). While design efforts continue to be made to conduct as much of the heat as possible through the media, the primary source of heat dissipation is through the slider. Unfortunately, as the heat is conducted through the slider, a portion of it passes through the read element and causes the read element to increase in temperature by 20°-30° C. or more. This elevation of the read element temperature ends up reducing the lifetime mean time to failure of the read element, since the mean time to failure falls exponentially with increasing temperature.
Some designs for read/write heads include internal diffusers to directly conduct heat along a particular path from the write element to the substrate, such as via a flat metal plate. While this has somewhat reduced the elevation in read element temperature, this approach has other disadvantages. First of all, due to the extra metal materials in the read/write head, the expansion of the various portions of the read/write head with temperature is more significant and this can result in pole tip protrusion, which is undesirable. Furthermore, having the large metal plate in the read/write head can degrade the write element performance due to eddy currents that are formed.
Another class of disadvantages resulting from the read element being located under the write element relates to electrical coupling, also known as read-write coupling. This is the capacitive coupling that occurs between the writer and the reader due to the electrical fields produced by the write element. In turn, this induces capacitive coupling across the read element. Since reading and writing do not occur simultaneously, the induced voltage across the read element tends to dissipate with time and does not appear to significantly affect performance during read operations. It does appear, however, that prolonged exposure of the read element to this electrical field can degrade the read element in terms of decreasing its lifetime or causing damage thereto.
Another class of disadvantages relating to the conventional reader under writer design relates to magnetic issues. With the commonly-used unshielded monopole write structure, placing the writer on top of the reader does not cause significant magnetic difficulties. However, the unshielded pole writer of the previously-discussed '949 patent has significant performance advantages due to higher field gradient which allows for higher linear bit density and it has a larger longitudinal field component which improves the effective write field strength which allows for the use of higher coercivity media with finer grains. Simply placing such a writer on top of a shielded GMR reader, however, results in the generation of excessive field under the writer shield because of flux coupling between the writer structure and the reader shields. This coupling can be reduced to an optimum level by placing a bucking coil between the writer structure and the reader structure as is taught in a commonly-owned U.S. patent application filed on the same day herewith and given U.S. patent application Ser. No. 10/701,909, entitled “Shielded Pole Writer”, the contents of which are incorporated herein by reference. This bucking coil is in series with the write coil and adds extra resistance and therefore power dissipation, thus contributing to heating and pole tip protrusion.
It is desirable to design/provide a read/write head which does not suffer from the above drawbacks. It is against this background and a desire to improve on the prior art that the present invention has been developed.